1. Field of the Invention
The present invention relates to an isolator/circulator used for the components"" protection and impedance matching of systems and terminals in mobile communication, personal communication, cordless telephones, and satellite communication, and more particularly, to a microstripline/stripline isolator/circulator having a propeller resonator.
2. Description of the Related Art
An isolator/circulator can operate in a predetermined direction, taking advantage of irreversibility of a permanent magnet and ferrite, and its frequency can be easily adjusted. A compact-sized isolator/circulator for terminals uses a microstripline, and a large-sized isolator/circulator uses a stripline. In recent years, the size of systems used for mobile communication, satellite communication, and millimeter waves has been reduced, and accordingly, it has been required to decrease the size, weight, and manufacturing costs of an isolator/circulator. In addition, the isolator/circulator has been required to have a low insertion loss, a high isolation, and a wide bandwidth.
FIG. 1 is a cross-sectional view of a conventional isolator/circulator including a stripline, and FIG. 2 is a cross-sectional view of a conventional isolator/circulator including a microstripline
Referring to FIG. 1, a conventional isolator/circulator includes a stripline 104 interpolated between an upper ferrite substrate 102a and a lower ferrite substrate 102b. A ground electrode 107 is formed at the top surface of the upper ferrite substrate 102a and at the bottom surface of the lower ferrite substrate 102b. An upper permanent magnet 103a is formed on the upper ferrite substrate 102a, and a lower permanent magnet 103b is formed under the lower ferrite substrate 102b. A thin iron plate 108 is interpolated between the upper permanent magnet 103a and the ground electrode 107 and between the lower permanent magnet 103b and the ground electrode 107.
Referring to FIG. 2, a conventional isolator/circulator includes a microstripline 104 formed on a ferrite substrate 102. A ground electrode 107 is formed at the bottom surface of the ferrite substrate 102. An upper permanent magnet 103a is formed on the microstripline 104, and a lower permanent magnet 103b is formed under the ferrite substrate 102. A thin Teflon(copyright) film 109 is interpolated between the upper permanent magnet 103a and the microstripline 104, and a thin iron plate 108 is interpolated between the lower permanent magnet 103b and the ground electrode 107.
The microstripline/stripline 104 that may be included in the conventional isolator/circulators shown in FIGS. 1 and 2 will be described in greater detail with reference to FIG. 3. As shown in FIG. 3, a circular resonator 100, which resonates at a predetermined frequency, is formed at the center of the microstripline/stripline 104. A first electrode 105a, a second electrode 105b, and a third electrode 105c are symmetrically formed along the circumference of the circular resonator 100 to connect the circular resonator 100 to an external circuit via their respective transfer tracks 106a, 106b, and 106c. In the case of an isolator, a load resistance of 50 xcexa9 (a load resistor having resistance of 50 xcexa9 is connected to the third electrode 105c. Here, reference numerals 102 and 103 represent a ferrite substrate and an upper or lower permanent magnet, respectively.
In a circulator having the microstripline/stripline 104, a signal of the external circuit is transmitted counterclockwise from the first electrode 105a to the second electrode 105b, from the second electrode 105b to the third electrode 105c, and from the third electrode 105c to the first electrode 105a. Here, the signal of the external circuit may be set to be transmitted clockwise. Accordingly, signals are circularly input into/output from a plurality of ports of the circulator.
In an isolator having the microstripline/stripline 104, a signal of the external circuit is transmitted counterclockwise from the first electrode 105a to the second electrode 105b and from the second electrode 105b to the third electrode 105c and then is extinguished passing through the load resistor connected to the third electrode 105c. In other words, while the signal of the external circuit is transmitted from the first electrode 105a to the second electrode 105b, the signal of the external circuit is not transmitted from the second electrode 105b to the first electrode 105a. Thus, the signal input into the isolator can be transmitted in a forward direction without being diminished but cannot be transmitted in a reverse direction. The signal of the external circuit may be set to be transmitted in a clockwise direction, like in the circulator.
In the microstripline/stripline 104, the resonant frequency of the circular resonator 100 is inversely proportional to the size of the circular resonator 100. Thus, in order to obtain a higher resonant frequency from the circular resonator 100, the circular resonator 100 is designed to have a smaller size. However, there is a limit in reducing the size of the circular resonator 100 to be capable of being used for ultrahigh frequency (UHF) for mobile communication or personal communication, and thus it is difficult to manufacture a compact-sized isolator/circulator.
FIG. 4 is a pattern view of a conventional microstripline/stripline. Referring to FIG. 4, a circular resonator 200 is formed at the center of a microstripline/stripline 204, and three slots 207 are formed along the circumference of the circular resonator 200 toward the center of the circular resonator 200. Three ports including a first electrode 205a, a second electrode 205b, and a third electrode 205c are symmetrically formed along the circumference of the circular resonator 200 to connect the circular resonator 200 to an external circuit via their respective transfer tracks 206a, 206b, and 206c. Here, reference numerals 202 and 203 represent a ferrite substrate and an upper or lower permanent magnet, respectively.
In the microstripline/stripline 204, a magnetic wall is formed at the slots 207 so that magnetic coupling quantity can be controlled. Accordingly, it is possible to manufacture an isolator/circulator having the same resonant frequency as an isolator/circulator having the microstripline/stripline 104 shown in FIG. 3 but having a smaller size by appropriately adjusting the length of the slots 207. However, in this case, in order to expand bandwidth, a bandwidth expansion circuit must be connected to the isolator/circulator, and thus there is a limit in manufacturing the isolator/circulator to be compact-sized at lower manufacturing costs. In addition, since the magnetic wall formed at the circular resonator 200 is used, the size of the upper or lower permanent magnet 203 is greater than the size of the circular resonator 200. Accordingly, ferromagnetic resonance line width (AH), which corresponds to loss of a magnetic body and amounts to at least the size of the circular resonator 200, exists. Thus, there is a limit in decreasing insertion loss.
FIG. 5 is a pattern view of a conventional microstripline/stripline. Referring to FIG. 5, a triangular resonator 300 is formed at the center of a microstripline/stripline 304, and three slots 307 is formed at the central portion of each side of the triangular resonator 300 toward the center of the triangular resonator 300 in order to control magnetic coupling quantity. Open-ring-shaped transfer tracks 306a, 306b, and 306c are formed extending from the vertexes of the triangular resonator 300 toward the outside of the triangular resonator 300. Three ports including a first electrode 305a, a second electrode 305b, and a third electrode 305c are symmetrically formed to connect the transfer tracks 306a, 306b, and 306c to an external circuit. Here, reference numerals 302 and 303 represent a ferrite substrate and an upper or lower permanent magnet.
Magnetic coupling occurs at the transfer tracks 306a, 306b, and 306c and the slots 307 of the triangular resonator 300 Due to the magnetic coupling, it is possible to manufacture a compact-sized isolator/circulator. In addition, magnetic coupling occurs between the transfer tracks 306a, 306b, and 306c and the first, second, and third electrodes 305a, 305b, and 305c and between the transfer tracks 306a, 306b, and 306c and the triangular resonator 300. Thus, impedance matching can be performed well, and a process of manufacturing an isolator/circulator can be simplified. However, like in the microstripline/stripline 204, there is still a limit in reducing the size of an isolator/circulator and insertion loss because the microstripline/stripline 304 takes advantage of magnetic coupling.
Various researches have been vigorously carried out to develop a compact-sized isolator/circulator having a microstripline/stripline, which can be effectively used at UHF that is generally used for mobile communication or personal communication. For example, according to U.S. Pat. No. 5,608,361 and U.S. Pat. No. 6,130,587, it is possible to manufacture an isolator/circulator to have a compact size, a wide bandwidth, and a low insertion loss; However, it is impossible to detect the state of a system including such an isolator/circulator. Specifically, in U.S. Pat. No. 6,130,587, a method of assembling an isolator/circulator is suggested. However, the method is not appropriate for mass production of an isolator/circulator because elements of an isolator/circulator are required to be appropriately aligned with each other.
To solve the above-described problems, it is a first object of the present invention to provide an isolator/circulator having a microstripline/stripline, which can have a low insertion loss, high isolation, a wide bandwidth, a compact size, a low price, a simple structure, and a light weight by solving the problems with the prior art and improving the prior art.
It is a second object of the present invention to provide an isolator/circulator having a microstripline/stripline, which is capable of allowing its state and the state of a system including itself to be detected.
To achieve the above objects, there is provided an isolator/circulator having a microstripline/stripline. The isolator/circulator includes a resonator including a plurality of symmetric propellers, which are capable of transmitting signals in a single direction, slot formation units formed between the propellers to allow magnetic walls to be symmetrically generated and each including a plurality of slots, transfer tracks for bandwidth expansion formed at a side of each of the propellers within the range of the distance (the circumscribed radius of the resonator) between the center of the resonator and the outermost edge of the propeller, and ports formed at the ends of the transfer tracks. The isolator further includes a load resistor which is connected to any of a plurality of ports formed in the microstripline/stripline.
It is preferable that the isolator/circulator further includes a coupler for detecting a reverse signal formed at any one of the plurality of the ports, and an indicator for indicating the reverse signal detected by the coupler in order to detect the state of the isolator/circulator and a system including the isolator/circulator. In the case of the isolator, the coupler is installed in any one of the plurality of ports, to which the load resistor is connected, and the indicator is connected to the coupler.
The frequency of the resonator may be controlled by controlling the ratio of the sum of the length of each of the slots and the distance (the inscribed radius of the resonator) between the center of the resonator and the outermost edge of the slot formation units with respect to the circumscribed radius of the resonator. Magnetic coupling quantity can be controlled by modifying the width and length of each of the slots while maintaining the inscribed radius of the resonator 0.6 times greater than the circumscribed radius of the resonator. Thus, the isolator/circulator may be compact-sized with a low saturation magnetization value.
The isolator/circulator having a stripline may be assembled as follows. A stripline is interpolated between upper and lower ferrite substrates. An upper case for a ground electrode is located over the upper ferrite substrate and has through holes, into which a plurality of screws can be inserted, and upper permanent magnet installed therein. A lower case for the ground electrode is located under the lower ferrite substrate and has grooves, into which the plurality of screws can be fit, and a lower permanent magnet installed therein. The radius of the upper and lower permanent magnets is less than the circumscribed radius of the resonator and is no less than the inscribed radius of the resonator so that usage of ferrite can be reduced. It is preferable that the radius of the upper and lower permanent magnets is equal to the inscribed radius of the resonator. As a result, low insertion low characteristics can be realized. A step difference as much as the thickness of the upper and lower ferrite substrates and the stripline exists in the lower case so that the upper and lower cases can be fit into each other to be in gear with each other. A groove, in which the load resistor will be installed, is prepared in the lower case of the isolator. The upper and lower cover simultaneously covers the upper and lower sides of the upper and lower cases assembled together without the need of additional assembling screws.
A method of assembling the isolator/circulator having a microstripline may be realized as follows. A microstripline is prepared on the ferrite substrate. An upper case for a ground electrode is located over the ferrite substrate and has through holes, into which a plurality of screws can be inserted and an upper permanent magnet installed therein. A lower case for the ground electrode is located under the ferrite substrate and has grooves, into which the plurality of screws can be fit and a lower permanent magnet installed therein. An upper and lower cover is formed to protect a magnetic field. Side covers is formed to constitute a closed circuit. SMA connectors are formed to connect the microstripline to an external circuit. A step difference as much as the thickness of the ferrite substrate and the microstripline exists in the lower case so that the upper and lower cases can be fit into each other to be in gear with each other. A groove, in which the load resistor will be installed, is prepared in the lower case of the isolator. The upper and lower cover simultaneously covers the upper and lower sides of the upper and lower cases assembled together without the need of additional assembling screws.
Since the operational frequency of the isolator/circulator according to the present invention can be controlled by forming a plurality of symmetric magnetic walls while maintaining the size of a propeller resonator, the size of the isolator/circulator can be reduced. Since a magnet having a smaller size than a resonator is used, it is possible to reduce insertion loss by decreasing the area of ferrite influenced by a magnetic field. It is possible to improve VSWR and isolation characteristics of the isolator/circulator by modifying slot formation units formed along the edge of the propeller resonator. Since transfer tracks for bandwidth expansion are formed within the range of the distance between the center of the propeller resonator and the outermost edge of the propeller resonator, it is possible to manufacture the isolator/circulator to have a compact size and a wide bandwidth.
Since a coupler is installed at an input/output port in order to detect a reverse signal and an indicator is installed to indicate the reverse signal detected by the coupler, it is possible to detect the state of an isolator/circulator and a system including the isolator/circulator by inserting a circuit for detecting a reverse signal or a reflection signal into the isolator/circulator. Also, it is easy to assemble the isolator/circulator and thus the isolator/circulator can be mass-produced at low costs.